Voice (sound) and pattern (image) recognition by a computer for interaction with an operator is now possible. It is highly desirable to extend a computer's senses to include the sense of touch for computer manipulation and recognition of objects. While some progress has been made in developing tactile sensors the sensors produced thus far are crude in comparison to the advances made in the art of computer recognition of sound and images.
Simple tactile sensors in which particular ones of an array of electrical membrane type switches operating in response to pressure have been devised. Such sensors are indicative of whether pressure has or has not been applied and provide no information which can be integrated into a feedback arrangement to control the magnitude of the applied pressure. While sensing of surface detail can be done using an array of membrane switches, much information respective to surface texture and shape of an object is lost due to the inherent threshold of mechanical switches. Surface and pattern information is generally acquired by adding visual adjuncts, such as television equipment monitored by an attendant, to complement the tactile arrangement. However, this is a costly alternative.
Other attempts have been made to solve the problem, such as the use of mechanical strain gauges placed in a tactile arrangement for measuring pressure. Arrangements of this type are somewhat successful in ascertaining pressure but suffer from the disadvantages of requiring calibration of the strain gauges and the inability to ascertain accurately the pattern of an object.
Conductive elastomers and the like whose conductivity changes as a function of applied pressure, have been used to fashion an array of tactile sensors in the form of robotic fingers. Sensors of this type operate properly and at first glance appear to be a solution to above-mentioned problems. However, these materials fatigue easily when flexed over a short duration, which, in turn, degrades the response of the material to the application and removal of pressure.
Advancements in the art of compliant touch sensitive surfaces include a bezel, such as plate glass, which is placed over the face of a cathode ray tube. Signals emitted by the cathode ray tube enter the glass plate bezel and become entrapped between the surfaces of the bezel by total internal reflection when touched. The trapped signals then travel to the sides of the plate glass bezel where photodetectors register the entrapment. Besides plate glass, flat compliant surfaces are used to enhance the injection of signals into the overlay. Signals emitted by a cathode ray tube become entrapped between the surfaces of the flat compliant overlay at a point in which the overlay is deformed.
Devices of this nature can be arranged as tactile sensors in which the entrapped light would be indicative of the pressure applied to the device. However, such devices cannot identify the pattern of the applied pressure due to inefficient modulation of light by the deformation of a flat compliant surface. Moreover, these devices show no initial response to pressure due to the operating characteristics of the flat compliant surface. As such, these devices are more suitable as compliant screens controled by a human operator rather than as tactile devices for robotic applications.